Heretofore, lead and lead alloys have been used as a material for a nuclear radiation shield, in terms of high density and excellent radiation-shielding ability. At the same time, the lead and lead alloys involves a problem about poor availability as a shield material for use in an area to be subjected to plasticity working, when the lead or lead alloy-based material has a large thickness, because of its hardly shaping ability during a deformation process. Recent years, an aggregate of thin fibrous lead strands, so-called lead wools, has been increasingly used as a lead-based shield material being capable of shaping. While the use of lead wools can facilitate deformation and shaping, the material becomes more reduced in density along with increase in the degree of deformation and causes a problem about deterioration in radiation-shielding performance. Moreover, lead itself is harmful to humans, and the use of lead has been increasingly restricted. Thus, there is the need for developing a lead-free material usable as a radiation shield.
A heavy-metal plate and a resin-based material prepared by kneading a radiation-shielding powder having a radiation-shielding ability as its own property, such as iron oxides have been used for shielding against electromagnetic radiation. However, these materials have difficulties in being shaped through a deformation process, and the resin-based material containing the radiation-shielding powder kneaded thereinto has another disadvantage about fragility and the need for paying particular attention to its handling.
So as to solve disadvantages of a radiation shield material as an alternative to the above conventional lead-based material and to meet the need for environmental public health and flexibility, a radiation shield material comprising a composite material consisting of a metal and an organic material is disclosed in Japanese Patent Laid-Open Publication No. 08-122492.
However, the fact of the matter is that the composite material consisting of the metal and organic material is liable to suffer breakage or cracks during handling and thereby required to pay particular attention to its handling as heretofore. While the strength or content of the organic material may be increased as measures against this problem, such measures will spoil its original flexibility and density, and lead to deterioration in radiation-shielding performance. Moreover, the composite material consisting of the metal and organic material disadvantageously catches fire easily in the event of a fire or abnormal overheating.